Process of agglomerating mixtures of fine ore and fuel in shaft furnaces



Feb. 27, 1923. 1,447,071.

C. GIESECKE. PR cEss 0F AGGLOMERATING MIXTURES or FINE one AND FUEL msum FURNACES.

I FILED SEN-25, I922.

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' ib/MM Blocks Carl G/esec/Ye Patented Feb. 27, 1923.

QNETED STAT-ES LMLWE Parser caries.

CARL GIESEGKE, or BAD HARZBURG, GERMANY.

PROCESS OF AGGLOMERATING MIXTURES OF FINE ORE AND FUEL IN FURNACES.

SHAFT Application filed September 26, 1922. Serial No. 590,679.

To all whom it may concern:

Be it known that I, CARL GIESEOKE, engineer, a citizen of Germany,residing at Bad Harzburg, Germany, have invented a certain new anduseful Improvements in Processes of Agglomerating Mixtures of Fine Oreand Fuel in Shaft Furnaces (for which I have filed "application inGermany, February 18, 1920), of which the following is a specification.

My invention relates to a process of agglomerating mixtures of fine oreand fuel in shaft furnaces.

The process of agglomerating blocks of line iron ore by means of smallcoke within shaft furnaces in some cases yields a prod uct which, inaddition to a high degree of rigidity, shows a very high degree ofporosity, as compared to the product ordinarily resulting from thesintering process. The sintering is always accompanied by a certainglazing by reason of a partial melting of the mass. In view of thesefacts I have made researches to ascertain under what conditions productshaving said desirable properties may be obtained, my object being tocarry out the process in such a way as to obtain the desirableproperties at will. In blast furnaces those agglomerates have thehighest value which, where the solidarity of the products is the same,are the least glazed.

I have found that very porous agglomerates are obtained where thefurnace is operated according to certain principles, the essentialfeature being that the piece or block which is not glazed in thesintering zone is thereafter brought intocontact with very hot air, fromtransform the protoxid or oxid-protoxid into oxid. By thus taking upoxygen the block is transformed in a manner similar to crystallization,which transformation-is effected uniformly throughout the block andresults in a cementing of the individual particles to the skeleton and acorresponding increase of the volume of the particles. However, theamount of oxygen taken up by the mass is small, so that the size of thepores is not materially reduced, while the increase in rigidity causedby the oxygen is material.

The object of this invention is to operate the furnace in such a waythat the process is which it takes up oxygen toregularly carried out andagglomerates are obtained which have the valuable propertieshereinbefore referred to. With this object in view, my inventionconsists in charging the shaft furnace with blocks having a smallquantity of fine carbon uniformly distributed therein, rapidly heating acomparatively low layer thereof above the combustion zone while slightlysintering the same, in order to cause reduction of the iron o-xid to theoxydul, and heating by means of gaseous fuel, such as flue gas,generator gas, mixed gas, or the like, plied to the combustion zone andassisted in burning. by means of ascending air.

In a modification of the process the agglomerates are subjected to ahigher reducing heat by having a larger amount of carbon admixedtherein, regulating the supply of gas above the combustion zone andwithin In the accompanying diagrammatic vertical sectional view of ashaft furnace suitable for carrying out my process, 1 represents thefurnace, of which the shaft preferably flares slightly downwardly andoutwardly. The furnace is charged (preferably continuously as by aconveyor 2) with blocks 3 which are formed of a mixture of fine ore anda small amount of fine coke. Near the surface of the column of blocks inthe furnace, ordinarily from three to six feet below said surface, gasunder pressure is supplied to the furnace through nozzles 4. The amountof gas supplied through the nozzles 4 may be controlled as by a valve 5.The products of combustion are drawn off at the top of the furnace byany suitable means, as by a suction fan 6, so that air, which may besupplied by nozzles 7 or other suit said gas being supcontinues as bymeans of a conveyor 8.

The advantages of my new process, as compared to the old method whereinthe ore is heated by means of solid fuel, are best illustrated by thefollowing example: Where the ore is heated by means of solid fuel carbonis burnt, but where it is heated by means of gas mainly carbon oxid isburnt,

the product of the combustion being in both cases carbon dioxid. Whenburning carbon to produce carbon dioxid one kilogram of oxygen isdeveloped.

808O- =3O3O calories.

But when burning carbon oxid to produce carbon dioxid one kilogram ofoxygen is developed.

(8080 2473) 4210 calories.

Therefore, in order to develop the same amount of heat by burning carbondioxid, only 72 per cent of the volume of air is necessary, as comparedto the volume of air required for burning carbon. The reduc-- tion inthe volume of air required makes it possible to preheat the air to ahigher temperature when ascending within the furnace and coming intocontact with the sintered blocks; and, when thus heated to highertemperature, the air causes a more intense re-oxidation below thecombustion zone, so much the more because, by reason of its diminishedvolume, it consumes less heat in raising its own temperature. Therefore,very hot air will cause the reoxidation with such a rise of temperaturethat the .air reaches its maximum temperature below the combustion zone,thus causing the sintering to take place below the combustion zone.However,

such sintering is limited to the desirable degree, because it depends onthe amount of oxygen passing into the ore under treatment, and theoxygen ceases'to permeate the ore as the density increases.

. As a matter of fact, with carbon oxid and carbon, the diiference ofthe temperatures of the preheated air is higher so far as the result isconcerned, than may be assumed from the above example, as will appearfrom the following calculation. It may be assumed that in one case theamount of small coke used in the process amounts to 8 per cent of thefinal sintered product, that 1 kilogram of small coke consumes 10 cubicmeters of air (having regard to the necessary excess of air), that thespecific heat of the sintered product is on an average 0.18,

T 1250-O.l8

For burning carbon oxid only 72 per cent of the volumeof air isrequired, which air is therefore heated when entering into thecombustion zone to T :126O C.

So far it has been assumed that the heat is transmitted without anyloss, which is practically impossible. The heat radiated from that partof the furnace which is below the combustion zone reduces the efi'ect ofthe preheating of the air, so that actually the above temperatures arenot attained, the

temperature being in case of solid fuel about 750 (1., if the furnace israpidly operated.

, Similarly the temperature of the air in case of gaseous fuel is lessthan 1260 C., and it is about from 1000 to 1050 0. Of course thetemperature of 1260 C. can not be attained, because it can in no case bemore than the sintering temperature, which is about 1250 C. However,there is a sufficiently intense reoxidation only where the temperatureis as high as just stated, whereas at the lower temperature of the air,where the firing is done by coke, reoxidation does not take place atall, such reoxidation being observed only where the old process ispracticed in connection with some products and where there has beenaccidental and irregular operation of the furnace.

High preheating of the air is particularly important, if it is desired,by reoxidation below the combustion zone, to raise the temperature ofthe sintered product for the purpose of partly solidifying the same. By0x1- dation of 1 kilogram of iron in the compound of Fef) to produce FeO 571 calories are set free. If it is assumed that in 1 kilogram of oreonly 0.2 kilogram of Fe have before been reduced to FeO and thereafterare reoxidized to Fe O 114.2 calories are set free. This heat raises thetemperature of the air and of the piece of ore the specific heat ofwhich may be set at 0.20 at the said temperature, by

If, before the beginning of the reaction the temperature of the air wasalready as high as 1000 (3., this slight increase is sufficient to raisethe ore to sintering temperature, which is not more than 1250 (1., whilethe temperature can be raised to 1302. Notwithstanding this there is nomelting, because the oxidation and the generation of tinguished from theknown heat cease as soon as the structure of the ore has been brought toa certain density. Therefore, the furnace can be operated in a verysimple manner.

Furthermore, the method has the advantage that, even a gas of lowheating capacity can be used, because it is not desired to raise thetemperature in the combustionzone and above the latter sufliciently tosinter the blocks. The amount of heat set free by! reoridation isconsiderably increased wlfen reducing iron oxid to metal, even if suchreduction is effected with only a very small part of the ore. What ismost important is that reoxidation in the same manner as reduction takesplace within the agglomerates, where also the heat is developed. Therebyhigh solidity is imparted to the individual agglomerates, and they haveless tendency to being welded together into large size blocks, as is thecase where the heat required for sintering is developed by burning solidor gaseous fuel between the agglomerates.

I am aware that it is known in the art to utilize for the purpose ofsintering, the heat set free by reoxidation of the ore which hadpreviously been reduced. My process is disprocesse first, in that Iobtain a product of high porosity, instead of slag, and large blocksinstead of small ones, second, in that I heat by means of completelyburnt gas, and third, in that I reduce by a small amount of carbonfinely divided in the ore.

I claim:

1. The herein described process of agglomerating fine ore, whichconsists in mixing the ore with finely divided carbon, heating the samein a shaft furnace bymeans of reducing gas admitted at a point near thesurface of the material and below the same at a temperature insufiicientto materiallysinter the material and reoxidizing the ore after it haspassed the combustion zone by means of hot air rising in opposition tothe ore.

2. The herein described process of agglomerating fine ore, whichconsists in mixing the ore with finely divided carbon, heating the samein a shaft furnace by means of reducing gas admitted at a point near thesurface of the material and below the same at a temperaturesubstantially not higher than is necessary for reducing the ore toprotoxid or metal and insufficient to materially sinter the material,and thereafter reoxidizing and sintering the ore after it has passed thecombustion zone by means of hot air rising in opposition to the ore.

In testimony whereof I have affixed my signature in presence of twowitnesses.

CARL GIESECKE. Witnesses:

WILHELM LEHRKE, WILLI FAHN.

